Recently, a data way system has come into use for input of data from a number of data input modules (e.g., temperature sensors) and transmission thereof to a number of data output modules (e.g., various meters on a concentrated indicator panels). In such a system, a series of data transmission lines connect a controller and the data modules to one another while making a loop. Each data module is given its own unique address, and a data is transmitted from an addressed data input module to an addressed data output module in a time-divided manner.
The addresses of the modules are specified by the controller. There is a case where the module addresses are provided into the controller from outside. Usually, however, the controller has a built-in address counter for specifying the module addresses. In the latter case, the more modules are connected to the data transmission lines, the longer are the intervals between the addressings of modules and, hence, the more difficult it is to transmit data at a higher rate. A sound module would have to be addressed at a frequency of 8 KHz or more in order to transmit sound with such a quality as is substantially equal to that of the sound obtained by a telephone. For addressing the modules at such a high frequency in the foregoing latter case, it is necessary either to reduce the number of the modules connected to the transmission lines or to increase the standard rate of clock in the controller. However, it is not desirable to reduce the modules because it would reduce the amount of data that can be input and output, and nor is it desirable to increase the clock rate because it would require the interface circuits of the modules to be modified accordingly and, hence, at least require the existing data way system to be substantially modified.